1. Field of the Invention
The present invention relates to an internal combustion engine system that uses a blended fuel consisting of hydrocarbon and alcohol.
2. Description of the Related Art
In recent years, compression ignition internal combustion engines such as homogeneous charge compression ignition internal combustion engine shave been studied in order to increase gas mileage of an internal combustion engine and reduce emissions. The compression ignition internal combustion engine introduces oxygen-containing gas and fuel capable of compression self-ignition into a cylinder for compression and self-ignition.
However, the compression ignition internal combustion engine has a problem that control of ignition timing is difficult unlike an internal combustion engine of a spark ignition type, and an operable area with stability is narrow. More specifically, this problem is that using a fuel with high ignitability may easily cause knocking when a required load of the engine is increased, and using a fuel with low ignitability may easily cause misfire when the required load of the engine is reduced.
In order to solve the problem, a technique has been known of mixing a fuel with high ignitability and a fuel with low ignitability and supplying the mixed fuels to the engine (for example, see Japanese Patent Laid-Open No. 2001-355471). According to this technique, a mixing ratio between the fuels is adjusted according to a required load of a compression ignition internal combustion engine, thereby allowing a stable operation relative to a wide range of required load. In this technique, however, the fuel with high ignitability and the fuel with low ignitability need to be separately prepared and housed.
On the other hand, a technique has been also known of using a single fuel, and oxidizing part of the fuel when a required load of a compression ignition internal combustion engine is increased, thereby generating ignitability inhibiting substance (for example, see Japanese Patent Laid-Open No. 2000-213444). More specifically, this technique is to oxidize part of a hydrocarbon fuel such as gas oil to generate ignitability inhibiting substance such as formaldehyde. However, partial oxidation of hydrocarbon such as the gas oil to generate formaldehyde requires a long-time reaction at high temperature.
As a fuel of an internal combustion engine, a blended fuel consisting of hydrocarbon and alcohol has been studied. When ethanol is used as the alcohol, the blended fuel can obtain a so-called carbon neutral effect by ethanol, thereby contributing to a reduction in an emission amount of carbon dioxide. The carbon neutral effect means that plants that are raw materials of ethanol absorb carbon dioxide through photosynthesis in its growing process, and thus burning ethanol to generate carbon dioxide is not considered to emit additional carbon dioxide as a whole.
However, when the blended fuel is supplied to a cylinder as a single fuel like gasoline and ignited by spark ignition, a sufficiently high efficiency cannot be obtained.